The present invention relates to: (a) compositions suitable as additives in the paper industry; (b) to preferred modified starches as components of such compositions; (c) to processes for providing such compositions; (d) to paper or paper products comprising such compositions; and (e) to processes for manufacturing paper or paper-like products which include such compositions.
Starches are widely used in the paper industry as wet end additives, as size-press additives, as binders in coatings and as adhesives. Advantages of the use of starch in paper can, for example, be the increased strength of the resulting paper, improved runnability, enhanced drainage, reduced amount of pollutants released, increased hydrophobicity or increased optical properties such as brightness and color.
An important property in practically all grades of paper is the above referred to paper strength. Not only do most papers require a minimum strength for the ultimate purpose, the paper must also be strong enough to permit efficient handling in manufacture. Many measures for the strength of paper are known. For example, the tensile strength is the greatest longitudinal stress the paper can bear without tearing apart. Since some paper products are subjected to wetting by water in their normal use, the wet tensile strength becomes important. Other well-known tests used to test strength parameters in paper are, for example, the bursting test, or Mullen test.
Natural starches can be used in the manufacture of paper and can be chemically or enzymatically modified. Modified starches often used are, for example, cationic, anionic, oxidized and phosphated starches. Cationic starches are often used to provide retention at the wet end and reduce the amount of pollutants released. Oxidized starch is known to have good film-forming properties and is, therefore, a favored material for coating and surface sizing.
Several problems are attached to the use of starches in the paper industry. For example, unsatisfactory strength increases may occur due to the limited amount of neutral or negatively charged starch that can be added since the starch has little or no attraction to the negative charge of the pulp.
Conventionally used, cationic starch has an attraction to the pulp to provide good retention. However, when cationic starch is added in an amount of more than several percent, the retention of starch in the paper layer is reduced and the starch is released from the paper and enters into the waste water.
It is of continuing interest to find compositions conventionally and cost effectively usable for high starch inclusion in paper or paper like products.
U.S. Pat. No. 4,097,427 relates to a process of cationization of starch in an aqueous medium in the presence of alkali metal hydroxide, cationic water-soluble polymers containing quaternary ammonium groups and an agent. The agents used are, for example, ammonium persulfate, hydrogen peroxide, hypochlorites, ozone, and certain organic peroxides and hydroperoxides. The modified starches thus prepared are used as wet end additives in papermaking to improve the dry strength of the paper.
U.S. Pat. No. 4,146,515 (Nalco Chemical Corp) discloses paper and other cellulosic material sized with a cationic starch prepared by forming an aqueous slurry of an oxidized starch, adding cationizing agent to the slurry and heating the slurry in a continuous cooker. More specifically, U.S. Pat. No. 4,146,515 relates to a process for the preparation of a cationic starch by forming an aqueous slurry of a lightly oxidized starch by starch with hypochlorite, adding a cationizing agent to the slurry and then heating the slurry in a continuous cooker. Suitable cationizing agents are, quaternized ethylene dichloride ammonia reaction products, dially/dimethyl ammonium chloride polymers and quaternized polyethyleneimines.
U.S. Pat. No. 4,818,341 describes a process for producing paper and paperboard of high dry strength by adding a mixture of a polymer modified potato starch to the paper stock and dewatering the paper stock with sheet formation. The potato starch is modified by heating an aqueous slurry of 100 parts by weight of potato starch with 1 to 20 parts by weight of cationic polymer which contains units of diallyldimethylammonium chloride, vinylamine or N-vinylimidazoline, at a temperature above the gelatinization temperature of potato starch in the absence of any agent, polymerization initiator of alkali.
A similar process for the production of paper, paperboard and cardboard is described in U.S. Pat. No. 4,940,514. In this process an enzymatically digested starch having a viscosity of from 20 to 2,000 mPa.s (measured in 7.5% strength aqueous solution at 45xc2x0 C.) is modified by treating with at least one of the cationic polymers specified above. The modified starch thus obtained is used as a wet end additive in the paper industry.
WO-A-98/31711 relates to a process for the production of starch which is modified with at least one cationic polymer. The polymer modified with starch is obtained by reacting an anionically modified starch with a cationic polymer or by reacting a natural starch or a non-anionically modified starch with a cationic polymer in the presence of an anionic modifier. Suitable anionic modifiers described include alpha-halogencarboxylic acids, inorganic or organic acids. The polymer modified starches are used as wet end additives in the production of paper and paper products.
U.S. Pat. No. 4,263,094 (BASF Wyandotte) discloses a cellulosic material such as paper or paperboard surface-sized with an aqueous dispersion of a combination of degraded starch derivative and a branched-chain, water dispersible polyester condensation product. The starch according to the invention is an alkaline-hypochlorite degraded starch having a decreased viscosity in comparison with the untreated starch.
EP776397 (Chemisolv Limited) describes a process of applying a high molecular weight polymer having a polyhydroxy backbone (e.g., starch) to a substrate, comprising adding to a solution of such material in anionic form a flocculent of oppositely charged form in order to insolubilise such material, and thereafter applying such insolubilised material to said substrate. The subject matter is disclosed as having particular application in respect of production of paper by adding to the slurry supplied in paper production an anionic starch and a cationic flocculent. Preferred flocculants disclosed are polyacrylamide cationic polymer, a copolymerised acrylamide/diallyldimethyl ammonium chloride or mannich acrylamide, or any other high molecular weight cationic (co) polymer carrying a permanently quaternized nitrogen.
JP54059416 describes the joint use of cationic polyamide-epichlorohydrin resin and anionic dialdehyde starch as dry and wet strength enhancer.
U.S. Pat. No. 4,925,530 (The Wiggins Teape Group Limited) discloses a process in which aqueous suspensions of papermaking fibers and filler are each separately treated with an anionic or a cationic polymer, after which the filler or the papermaking fiber is treated with a polymer of opposite charge to that used in the initial treatment. The initial treating polymer is characterized as preferably a papermaking retention aid or flocculent, e.g., a cationic polyacrylamide or an amine/amide/epichlorohydrin copolymer, in the case of cationic materials, or an anionic polyacrylamide, in the case of anionic materials. The further treating polymer is characterized as preferably an anionic or cationic starch, depending on the charge of the initial polymer.
WO9831740 (BASF AG) discloses starches with improved retention on cellulose fibers, useful as dry paper strength agents and as draining and retention acids, which are prepared by treating dry, flowable starch with an aqueous solution of cationic polymers and drying.
DE19701523 (BASF AG) describes a starch, which has been modified with at least one cationic polymer and a method for producing the same. The method for producing the modified starch includes the reaction of an anionic starch with a cationic polymer. Alternatively the modified starch can be prepared by reacting a native starch or a non-anionically modified starch with a cationic polymer in the presence of an anionic modifier.
U.S. Pat. No. 4,006,112 (Standard Oil Company) describes a polyester of a trimellitic acid compound having an average molecular weight under about 4000 and an acid number of at least 35 and starch paper sizing composition containing said polyester. Suitable starch sizes can be based on e.g., corn or wheat starch. Prior to use, the starches are modified, such as by alkaline-hypochlorite oxidation, acid or enzyme thinning and/or derivation to a low DS (degree of substitution).
According to the present disclosure a composition is provided comprising the result of combining a starch component, as defined, with a polymer component, as defined. In general, the preferred starch component comprises a starch having polymer-reactive carbonyl functionality therein, typically and preferably aldehyde functionality detectable by a Tollen""s test; and, the preferred polymer component is one having aldehyde-reactive functionality.
The starch component may be provided by oxidizing starch. Preferred oxidizing agents and conditions are characterized below.
Preferably the starch component is one having a reactive carbonyl functionality of at least 5 microequivalents per gram, more preferably at least 10 microequivalents per gram, and typically not more than 300 microequivalents per gram.
Preferably the polymer is one having reactive groups selected from primary amine groups and secondary amine groups. Typically and preferably the polymer component comprises a polyvinylamine polymer.
Preferred starch components and polymer components are characterized in more detail below.
The current disclosure also concerns methods of papermaking. Advantageous methods of papermaking are conducted using compositions as characterized herein. In some instances, high starch inclusion can be accomplished without the use of a sizing press step in the papermaking operation.
The current disclosure also concerns preferred paper materials, and paper products made in accord with the preferred processes characterized.
A. General Characterizations
According to one aspect, the present invention concerns provision of compositions in the form of starch/polymer combinations. Typical, preferred, starch/polymer combinations as described herein are of one of two types:
1. A preferred adducted combination of starch/polymer; or,
2. A preferred mixture, or combination, of starch and polymer which, although not in a form of an adducted combination, is in a combination that when appropriately introduced into a process such as a papermaking process, for example through a jet cooker, will form an adducted combination of the starch and polymer.
In general, the starch/polymer combinations comprise the result of combining:
(a) modified starch which includes a polymer reactive carbonyl functionality, typically aldehydic functionality, detectable by a Tollen""s test; and
(b) natural and/or synthetic reactive polymer component; i.e., polymer component having a carbonyl reactive functionality, typically aldehyde reactive functionality.
When it is said that the starch/polymer combinations comprise xe2x80x9cthe result of combiningxe2x80x9d the components characterized, unless specified it is not meant that the composition is necessarily reacted to form an adducted combination. Alternatively stated, the phrase xe2x80x9cthe result of combiningxe2x80x9d, without further limitation, is meant to refer to the components having been brought together, without regard to whether they have been reacted; that is, without regard to whether the carbonyl functionality in the modified starch is in fact reacted with the carbonyl reactive functionality in the polymer component.
Further, the term xe2x80x9cthe result of combiningxe2x80x9d is not meant to indicate specifically the method of combination, conditions of combination, or limitation on other additives, unless otherwise limited or specified.
Thus, as indicated above, the combinations may be xe2x80x9cadducted combinationsxe2x80x9d, or in certain instances may be mixtures which, when used, will form adducted combinations. Herein the term xe2x80x9cadducted combinationxe2x80x9d, and variants thereof, is meant to refer to a combination in which the starch component and the polymer component are chemically associated and are not merely mixed. That is, the term xe2x80x9cadductedxe2x80x9d is not meant to refer to compositions in which the starch component and polymer component are merely mixed, but are not chemically associated. Herein, the xe2x80x9cadducted combinationxe2x80x9d will be sometimes be alternatively termed xe2x80x9cpolymer modified starch.xe2x80x9d
When it is said that the starch component and the polymer component are combined to form an xe2x80x9cadducted combinationxe2x80x9d, no specific characterization or limitation on the nature of the chemical interaction between the two components is meant, unless further characterization is provided. Thus, the interactions or attractions may be ionic, they may be covalent, or they may be a combination of both. In general, however, the requirement that the starch component have a polymer reactive carbonyl functionality is meant to refer to a functionality which, under appropriate conditions, is capable of forming covalent interactions with carbonyl reactive functionality in the polymer component; and, when it is said specifically that the polymer component has a carbonyl reactive functionality, it is meant that the polymer component contains functionality capable of covalent reaction with the reactive carbonyl functionality in the starch. Thus, when appropriate conditions are utilized in association with combinations according to the present disclosure, at least to some extent covalent interaction between the starch component and the polymer component are expected.
It is noted that in many instances an ionic interaction between the starch component and the polymer component will also occur. This will occur for example when the starch component includes anionic groups, such as carboxyl functionalities, and the polymer component contains cationic groups, such as various amine groups or protonated amine groups.
Thus, in xe2x80x9cadducted combinationsxe2x80x9d according to the present disclosure, both covalent interactions and ionic interactions may be present, although the term xe2x80x9cadducted combinationxe2x80x9d by itself is not meant to refer to a specific level of interaction of either type.
1. The Starch Componentxe2x80x94Generally
An aspect to the present invention is the provision of preferred starch components for use in forming preferred adducted combinations of starch/polymer.
In general, when defined with respect to polymer reactive carbonyl functionalities, typically aldehyde groups, preferred usable starches in accord with the present principles are modified starches which are can be characterized as follows:
(A) When evaluated by the Tollen""s technique described below, in connection with Experiment 7a for bulk analysis, the starch component has at least 5 microequivalents of aldehyde groups per gram of starch; typically and preferably at least 10 microequivalents/gram, and generally an amount within the range of 20 to 300 microequivalents/gram starch.
(B) When the starch component is in a form that also includes carboxyl groups, it preferably has a ratio of carbonyl groups to carboxyl groups of at least 1:1, typically at least 2:1, and generally within the range of 2.5:1 to 5:1; when the carbonyl groups are evaluated by the Tollen""s test of Experiment 7a and the carboxyl groups are measured by the potentiometric test of Experiment 8.
A preferred usable and convenient manner for providing usable modified starches or starch components, is through oxidation of starch. In general, a manner in which to characterize such an oxidized starch is with respect to the type of oxidizing agent used and/or the amount of oxidizing agent used. When characterized in this manner, in general the oxidizing agent or agents used to prepare the starch should be one (or a mixture) which at least generates detectable levels of reactive carbonyl moities (aldehydic or ketonic) in the resulting starch, whether or not there is also generated carboxyl functionality.
Herein below, a variety of usable oxidizing agents are provided. Preferred ones comprise periodates and hypochlorites. In general, hypochlorites create both carboxyl and carbonyl components, when utilized. Periodates, on the other hand, generally create only carbonyl moities in the starch.
Of the periodates, generally sodium periodate is preferred; and, of the hypochlorites, generally sodium hypochlorite is preferred.
In general, herein the level of oxidant is defined in at least one of two manners. A first is through weight percent oxidant used, based on dry weight of starch. When defined in this manner, typically and preferably the amount of oxidant is at least 0.01% by wt. and not more than 5.0% by wt., based on the wt. of starch. Typically and preferably it is within the range of 0.1%-3.0%, by wt. of starch. Most preferably, it is within the range of about 0.3%-3.0%, by wt. of starch.
When the oxidant is a chlorine oxidant, for example a hypochlorite, herein the oxidant level is sometimes defined with respect to available chlorine percent, based on wt. of starch. The term xe2x80x9cavailable chlorinexe2x80x9d in connection with hypochlorite oxidants, is a term used to refer to the amount of chlorine, by wt. %, determined to be present when titrated in accord with a procedure such as that described in the Chlorine Institute Pamphlet 096 Sections 4.3 and 4.5. When defined in this manner, preferred oxidation conditions are those using at least 0.005% available chlorine by wt. of starch, typically at least 0.05% available chlorine by wt. of starch, and preferably not more than 3.0% available chlorine by wt. of starch. Typical and preferred conditions will be about 0.15%-1.5% available chlorine, by wt. of starch. Defining oxidant level by available chlorine level is a common practice for oxidations with hypochlorites.
2. The Natural or Synthetic Reactive Polymer Componentxe2x80x94Generally
In general, the natural or synthetic reactive polymer component may comprise any polymer or mixture of polymers suitable for, and capable of, forming preferred adducted combinations with the modified starch component. That is, the usable polymers are reactive polymers. In this context, the term xe2x80x9creactive polymerxe2x80x9d is meant to refer to polymer components that contain groups capable of reacting with reactive carbonyl groups in the starch, through covalent reaction and not merely ionic interaction, to form adducted combinations; or, to the residue of a polymer component which has already been reacted with the starch component to form an adducted combination.
It should be noted that the characterization above given with respect to xe2x80x9creactive polymerxe2x80x9d component does not require reactive polymer to have in fact reacted through covalent interaction. Rather it requires the reactive polymer to include functionality capable of covalent interaction with carbonyl groups in the starch. The level to which such covalent interactions actually occur when the combination is formed, will depend upon the conditions of combination.
Herein the term xe2x80x9cnatural polymerxe2x80x9d and variants thereof, is meant to refer to a polymer derived from a natural polymer source, for example, a plant or animal source. The term xe2x80x9cnatural polymerxe2x80x9d is meant to include within its meaning such polymers which have been modified by various processing steps, from the natural state. In this context, the processing steps may be chemical, biochemical, or mechanical steps. For example, the term xe2x80x9cnatural polymerxe2x80x9d includes glutens and modified glutens.
Herein the term xe2x80x9csynthetic polymerxe2x80x9d and variants thereof, without more, is meant to have its ordinary meaning in the polymer art; i.e., a non-natural polymer typically prepared by polymerizing smaller molecules.
In general, to be reactive, the polymer should comprise one or more functional groups capable of reacting with carbonyl (for example, aldehyde) functionality in the starch. Included among these functional groups are reactive amine groups. Typical reactive amine groups are primary amine groups, although secondary amine groups will also be reactive in some situations. In general, tertiary amine groups and quaternary amine groups are not reactive within this definition.
The polymer may also include groups capable of interacting ionically with carboxyl groups in the starch during adduct formation. A variety of groups are capable of doing this, including primary and secondary amine groups, protonated amine groups, tertiary amine groups, and quaternary groups. Of course, a polymer group which is only capable of interacting with a starch through an ionic interaction is not a carbonyl-reactive functionality, or aldehyde-reactive functionality, within the meaning of those terms as used in this disclosure.
The starch/polymer combination can be provided by merely mixing together a starch component as defined and a polymer component as defined. Such a mere mixing will result in a combination which is not an adducted combination, however, unless appropriate conditions are provided during the step of combination, or in follow up treatment.
In order to ensure an adducted combination, generally appropriate conditions of heat, and intimate interaction, are required. Conditions usable to accomplish this are provided herein, and are also apparent from the experiments. It is noted that if the combination is merely a mixing of the components, such a combination will be subjected to adequate conditions to result in a reacted combination or adducted combination, if the mixture is introduced into a papermaking process through a typical starch cooking operation, such as a jet cooker.
It is expected that after subjection to starch cooking conditions, combinations according to the present disclosure would include at least the following: reacted starch/polymer combinations; non-reacted starch; and, non-reacted polymer. That is, the term xe2x80x9cadducted combinationxe2x80x9d is not meant to refer to a composition which only comprises molecules resulting from reactive associations between the starch and the polymer; non-reacted materials, for example, may also be present.
Typical preferred natural or synthetic polymer components will be polymers comprising reactive primary amine groups.
B. Preparation of the Starch Component
A preferred method for preparing the starch component is by oxidizing starch in a slurry, for example in an aqueous medium.
One preferred approach is to oxidize natural starch with oxidizing agent selected from the group consisting of: periodate(s); hypochlorite(s); ozone; peroxide(s); hydroperoxide(s); hydrogen peroxide; persulfate(s); percarbonate(s); and, mixtures thereof (with or without catalyst). Examples of usable agents include: sodium periodate; potassium periodate; sodium hypochlorite; calcium hypochlorite; hydrogen peroxide; sodium persulfate; ammonium persulfate; and potassium persulfate. The more preferred agents are sodium periodate, potassium periodate, sodium hypochlorite and calcium hypochlorite. Preferred amounts were characterized above.
As indicated to above, when the oxidation is a hypochlorite oxidation, the starch will be rendered lightly negatively charged, since hypochlorite oxidations do generate carboxyl groups, as well as carbonyl groups. However, when the oxidation is a periodate oxidation, in general the starch will not become lightly negatively charged, since periodate oxidations of starch typically only generate carbonyl groups and not carboxyl groups.
The preferred oxidizing agents are the hypochlorites. In certain preferred processing, for example, when the oxidant is a hypochlorite, the conditions under which the starch is oxidized will typically be alkaline. Typical conditions would be a solution having a pH ranging from about 7.5 to 13, preferably 7.5 to 12, most preferably about 8 to 11. The conditions can be rendered alkaline by, for example, using NaOH as a base to buffer the system.
After oxidation, if desired, the oxidized starch can be isolated from the reaction mixture and be dried to a product which has nearly the same particle diameter as the natural starch before the oxidation. However, as shown in Experiment 24, it is also possible to directly react the oxidized starch with the natural or synthetic polymer component, without isolation of the oxidized starch from the reaction slurry resulting from the oxidation reaction.
The oxidation reaction can be conducted at a variety of starch concentrations and under a variety of conditions. For typical processing, preferably the temperature of the oxidation is maintained below a gelatinization temperature of the starch. The gelatinization temperature is the temperature at which the birefringence of the starch grain disappears. For a typical natural starch, the gelatinization temperature would be within the range of about 55xc2x0 C. to 70xc2x0 C. For typical processing, the oxidation of the natural starch will be carried out at a temperature no higher than about 55xc2x0 C., typically within the range of 10xc2x0 from 55xc2x0 C. Preferred oxidations are conducted with temperatures no greater than about 40xc2x0 C., and typically within the range of 20xc2x0 C.-40xc2x0 C., inclusive.
Typical reaction conditions will be selected to complete the oxidation by a total or near total consumption of the oxidizing agent, preferably within a period of no greater than about 24 hours, typically within a time period of seconds to several minutes. A wide variety of starches from natural sources, or processed after being derived from natural sources, can be used. Indeed, the starch material may be derived from root, tuber, or cereal starch sources. Examples of usable starches include maize (corn) starch, wheat starch, potato starch, rice starch, tapioca starch, sorghum starch, sago starch, cassava starch, waxy maize starch, and mixtures of these starches. According to certain preferred applications, generally in accord with procedures described below, maize or wheat starch, or mixtures thereof, or starch mixtures including at least 70% by wt. of maize and/or wheat starch, are preferably used. The starch material may be chemically, physically, or enzymatically modified, from its natural state. However, it is advantageous that the process can be conducted with natural starch. An example of this is use of maize starch obtained directly from corn wet milling, without modification, and thus without significant added cost.
C. The Polymer Component
In general, the polymer component may be either natural polymer(s), synthetic polymer(s) or mixture(s) thereof. As indicated above, the required characteristic of the polymer component is that it at least comprises groups capable of reaction with carbonyl groups (aldehyde or ketone) in the starch component, through covalent interaction, to form the adducted combination. Such polymers will generally be referenced as polymers that contain carbonyl-reactive functionality, or more specifically as containing aldehyde-reactive functionality. In some instances, they may be referred to as xe2x80x9creactive polymers.xe2x80x9d Preferred carbonyl-reactive (or aldehyde-reactive) functionalities comprise reactive amine groups. Typical reactive amine groups are primary or secondary amine groups. In general, it is believed that primary or secondary amine groups are reactive with carbonyl groups in the oxidized starch, through formation of imino groups, i.e., Schiff bases.
Consistent with the above, then, typical natural or synthetic polymers usable to form adducted combinations according to the present invention are ones which include, within the polymer molecules, a sufficient amount of functionality to form the bond (covalent) with the oxidized starch molecule. These reactive groups, again typically primary and/or secondary amine groups, can be bonded directly to the polymer backbone, or they may be substituents on groups dependent from the polymer backbone.
The polymer component may comprise a homopolymer, (i.e., a polymer formed from a single monomer), or they may comprise a copolymer (i.e., a polymer formed from more than one monomer). The polymer component can be a mixture of such polymers.
The specific amount of reactive groups for the starch component found in each polymer molecule, on average, is not critical. In general all that is required is that the polymer have enough reactivity for the conditions of reaction with the starch component.
Suitable synthetic polymers include polymers consisting of, or at least containing, monomer residue units of vinyl amine. Herein, in this context, the term xe2x80x9cmonomer residue units of vinyl aminexe2x80x9d or variants thereof, is meant to refer to a polymer which has in its backbone: (a) residues resulting from reaction, in polymer formation, of a vinyl amine; or, (b) a group structurally equivalent to one which would result from using a vinyl amine as a monomer. By the latter, it is meant that the unit may have derived from a different reactant, but which is in the chemical form of a vinyl amine residue unit. A preferred such polymer is a polyvinylamine (PVAm) (or a copolymer of vinylamine monomers or oligomers), typically having an average molecular weight of at least about 1xc3x97103 gram/mol, preferably of at least about 1xc3x97103 gram/mol and up to 30xc3x97106 gram/mol. Preferred such polymers are ones having a charge density of about 10-15 meq/g (milliequivalents/gram). In this context, xe2x80x9ccharge densityxe2x80x9d means amount of positive charges per gram of polymer.
Polymers belonging to this group are known for example from U.S. Pat. Nos, 4,421,602 and 4,444,667 (incorporated by reference). They are obtainable by homo or copolymerization of N-vinylformamide and hydrolysis of these copolymers with acids or bases or enzymatically. During hydrolysis the formyl group of the homopolymers of N-vinylformamide or of the copolymers of N-vinylformamide is split off under formation of a primary amino or ammonium group. The N-vinylformamide units in the polymers can be partially or completely hydrolyzed. The degree of hydrolysis can be 1 to 100, preferably 5 to 100 or 10 to 95%. If a homopolymer of N-vinylformamide is hydrolyzed at a degree of 100%, the polymer obtained is polyvinylamine. If the hydrolysis is carried out partially, the polymer obtained contains N-vinylformamide units and vinylamine units depending of the degree of hydrolysis.
Polymers containing monomer residue units of vinyl amine are also obtainable from copolymers of N-vinylformamide with one or more comonomers and hydrolysis of the copolymers. The degree of hydrolysis of the polymerized N-vinylformamide may the same as specified above for hydrolysis of the homopolymers of N-vinylformamide. Suitable comonomers are, for example, vinyl esters of saturated carboxylic acids of 1 to 6 carbon atoms, e.g., vinyl formiate, vinyl acetate, vinyl propionate and vinyl butyrate, esters of ethylenically unsaturated mono or dicarboxylic acids containing 3 to 6 carbon atoms, e.g., methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate and monoesters of acrylic and methacrylic acid with polyalkylene glycols having a molecular weight of from 200 to 10,000 preferably 400 to 2,000. Further examples of suitable monomers are esters of the said acids with aminoalcohols such as dimethylamino ethyl acrylate, dimethylamino methycrylate, dimethylaminopropyl acrylate and dimethylaminopropyl methacrylate.
Other suitable comonomers are unsaturated amides such as acrylamide, methacrylamide and N-alkylmonoamides and N-alkyldiamides having alkyl radicals of 1 to 6 carbon atoms, e.g., N-methylacrylamide, N,N-dimethylacrylamide, N-methylmethacrylamide, N-elhylmethacrylamide, N-isopropylacrylamide, N-n-propylacrylamide and basic acrylamides such as dimethylaminoethylacrylamide, dimethylaminomethacrylamide, dimethylaminopropylacrylamide and dimethylaminopropylmethacrylamide.
Other suitable comonomers are vinyl ethers having alkyl groups of from 1 to 18 carbon atoms, e.g., methyl vinyl ether, ethyl vinyl ether, n-propylvinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, n-pentyl vinyl ether and n-hexyl vinyl ether, or vinyl ethers having aromatic substituents such as phenyl vinyl ether or benzyl vinyl ether.
Other suitable comonomers are N-vinyl pyrrolidone, D,-vinyl caprolactam, acrylonitrile, methacrylonitrile, N-vinylimidazole and substituted N-vinylimidazoles such as N-vinyl-2-methylimidazole, N-vinyl-4-methylimidazole and N-vinyl-2-ethylimidazole, N-vinylimidazoline, N-vinyl-2-methylimidazoline and N-vinyl-2-ethylimidazoline. N-vinylimidazoles and N-vinylimidazolines are used not only in the form of the free bases but also in a form neutralized with mineral acids or with organic acids or in quaternized form, quaternization preferably being carried out with dimethylsulfate, diethylsulfate, methyl chloride or benzyl chloride.
The molar mass of preferred usable polymers containing the residues of vinylamine monomers are, for example, from 1,000 to 10 million, preferably form 5,000 to 5 million (determined by light scattering). This molar mass corresponds, for example, to K values of from 5 to 300, preferably from 10 to 250 (determined according to H. Fikentscher in 5% strength by weight aqueous sodium chloride solution at 25xc2x0 C. and at a polymer concentration of 0.5% by weight). The polymers containing the residues of vinylaine monomers are preferably used in salt-free from. Salt-free solutions of such polymers can be prepared, for example, from the salt-containing solutions which for instance are obtained by hydrolysis of N-vinylformamide units containing polymers with acids such as hydrogen chloride or sulfuric acid, with the aid of ultrafiltration through suitable membranes with separation limits of, for example, 1,000 to 500,000, preferably from 10,000 to 300,000 dalton.
If desired, the copolymers may also contain additionally polymerized monomer units having at least two ethylenically unsaturated double bonds. Such monomers are usually used in the copolymerization as crosslinking agents. Thus, N-vinylformamide or mixtures of N-vinylformamide with 1 to 99 mol % of other monoethylenically unsaturated monomers can be additionally copolymerized with at least one crosslinker in an amount of from 0 to 5 mol %.
The above polymers of N-vinylformamide are hydrolyzed to form polymers containing vinylamine units. Preferred polymers of this group are homopolymers of vinylamines and hydrolyzed copolymers of N-vinylformamide and vinylacetate containing vinyl amine units and vinyl alcohol units. The vinyl alcohol units are formed by hydrolysis from vinylacetate units contained in the polymer.
Other suitable polymers containing the residues of vinylamine monomers are obtainable from polymers containing N-vinylformamide grafted on polysaccharides or polyalkylene glycols. The N-vinylformamide grafted polymers are hydrolyzed under formation of vinylamine units containing polymers. The polymers belonging to this group are known for example from U.S. Pat. Nos. 5,334,287, 6,048,945 and 6,060,566 (incorporated by reference). Usually per 100 parts by weight of starch, a polyalkylene glycol such as polyethylene glycol, polypropylene glycol or block polymers of ethylene and propylene glycol, or a vinylester are grafted with from 0 to 100, preferably from 5 to 95 parts by weight of N-vinylformamide and are then completely or partially hydrolyzed.
Other usable polymers which contain reactive amino groups are polyethyleneimines. They are prepared, for example, by polymerizing ethyleneimine in aqueous solution in the presence of acid-eliminating compounds, acids or Lewis acids. Polyethyleneimines have, for example, molar masses of up to 2 million, preferably 200 to 500,000. Polyethyleneimines having molar masses of from 500 to 100,000 are particularly preferably used. Water soluble crosslinked polyethyleneimines which are obtainable by reacting polyethyleneimines with crosslinking agents such as epichlorohydrin or bischlorohydrin ethers of polyalkylene glycols with from 2 to 100 ethylene oxide and/or propylene oxide units or blockpolymers containing blocks of units of ethylene oxide and propylene oxide are also suitable.
Suitable amino- and/or ammonium-containing polymers also include polyamidoamines grafted with ethyleneimine. These polymers can be obtained, for example, by first condensing dicarboxylic acids with polyamines and then grafting the polyamidoamines thus obtained with ethyleneimine. Suitable polyamidoamines are obtainable by reacting dicarboxylic acids of 4 to 10 carbon atoms with polyalkylenepolyamines which contain from 3 to 10 basic nitrogen atoms in the molecule. Examples of suitable dicarboxylic acids are succinic acid, maleic acid, adipic acid, glutaric acid, sebacic acid and terephthalic acid. In the preparation of the polyamidoamines, it is also possible to use mixtures of dicarboxylic acids as well as mixtures of a plurality of polyalkylenepolyamines. Suitable polyalkylenepolyamines are, for example, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dipropylenetriamine, tripropylenetetramine, dihexamethylenetriamine, aminopropyl ethyl endiamine and bisaminopropylethylenediamine. For the preparation of the polyamidoamines, the dicarboxylic acids and polyalkylenepolyamines are heated to relatively high temperatures, for example, to temperatures of from 120 to 220xc2x0 C., preferably from 130 to 180xc2x0 C. The water formed in the condensation is usually removed from the system. In the condensation it is also possible to use lactones or lactams of carboxylic acids of 4 to 18, preferably 6 to 12 carbon atoms. For example, from 0.8 to 1.4 mol of polyalkylenepolyamine are used per mol of dicarboxylic acid. The polyamidoamines thus obtained are grafted with ethyleneimine using for example, per 100 parts by weight of polyamidoamine 1 to 50 parts by weight of ethyleneimine. The grafting of the ethyleneimine is carried out in the presence of acids or Lewis acids, such as sulfuric acid or boron trifluoride etherates at, for instance, from 80 to 100xc2x0 C. Polyamidoamines can be crosslinked before being grafted with ethyleneimine. Suitable crosslinking agents are, for example, epichlorohydrin, bischlorohydrinethers of polyalkyleneglycols and bisepoxides of chlorohydrinethers of polyalkyleneoxides. Compounds of this type are described for example in DE-E-24 34 816.
Polyallylamines are also suitable synthetic reactive polymers. Polymers of this type are obtained by homopolymerization of allylamine, preferably in a form neutralized with acids or in quaternized form or by copolymerization of allylamine with other monoethylenically unsaturated monomers which are described above as comonomers for N-vinylforamide. The K values of these polymers is of from 30 to 300, preferably from 100 to 180 (determined according to H. Fikentscher in 5% strength by weight aqueous sodium chloride solution at 25xc2x0 C. and at a polymer concentration of 0.5% by weight). At a pH of 4.5, they have, for example, a charge density of at least 4 meq/g of polyelectrolyte.
Other suitable cationic synthetic polymers having reactive amino groups are polylysines. Such polymers are obtained by condensing lysine alone or together with other compounds such as amines or lactames. Compounds of this type are disclosed in U.S. patent application Ser. No. 09/13123 (incorporated by reference).
Further synthetic polymeric compounds containing reactive amino groups are polymers containing aminoethyl acrylate units and polymers containing aminoethyl methacrylate units. Aminoethyl acrylate and/or aminoethyl methacrylate may be polymerized alone or in combination or together with other monoethylenically unsaturated monomers. The molecular weight of the polymers is, for example, of from 1,000 to 5 million, preferably of from 5,000 to 500,000.
Other suitable cationic synthetic polymers having reactive amino groups are condensation products of piperazine, 1-(2-aminoethyl)piperazine, 1,4-bis(3-aminopropyl)piperazine and mixtures thereof with crosslinkers. The condensation reaction is carried out in an aqueous medium. Condensation products of this type are disclosed in U.S. Pat. No. 6,025,322 (incorporated by reference).
Dendrimers containing reactive amino groups are also suitable for the production of polymer modified starches of the present invention.
D. Formation of the Starch/Polymer Combination
As indicated above, it is postulated that when the adducted combination is formed from a reactive carbonyl containing starch (typically an oxidized starch) and a polymer comprising reactive groups, for example primary or secondary amino groups, the adducted combination at least in part results from formation of imino groups, i.e., formation of Schiff bases. Such an interaction would be a covalent interaction. It is also postulated that when the starch is one which also includes anionic groups such as carboxyl groups, then typically an additional interaction will occur with the polymer, i.e., an ionic interaction, since the types of polymers characterized above are generally cationic polymers.
Both covalent and ionic interactions will be present in many typical starch/polymer combinations according to the present disclosure, provided both reactive carbonyl moities (typically aldehyde moities) and anionic (carboxyl) moities are present in the starch from which the combination is formed. However, in general, it has been observed, as demonstrated in the experiments, that the presence of at least some carbonyl (typically aldehydic) component in the starch, capable of covalent interaction with a polymer, is preferred.
Typically and preferably the amount of reactive polymer provided in the combination is no more than about 5.0%, by wt. of starch, typically at least 0.1%, and generally within the range of 0.5 to 2.5%. In this manner, although the starch is modified with respect to its interactive characteristics with the paper and with respect to its behavior in the papermaking process, it is readily handleable in the same manner as conventional starch additives.
As indicated above, the oxidized starch can be isolated from the oxidation reaction, before reaction with the polymer. Also as indicated, however, if desired after oxidation, the slurry of the oxidized starch can be directly reacted with the synthetic polymer. This latter approach may be convenient, if it is desired to carry out the formation of the adducted combination in the same apparatus as that in which the starch slurry was oxidized; for example by adding the cationic polymer to the aqueous solution, after the oxidation. A typical approach would be to (a) add reactive polymer to the slurry, (b) raise the temperature of the slurry up to at least the boiling point of water, and, (c) after sufficient reaction time, isolate the adducted combination or polymer modified natural starch, by spray drying or spray-granulation, with the resulting solid (adducted combination) being separated in a conventional manner, for example, by cyclonic separation (i.e., in a cyclone).
The reaction to form the adducted combination can be conducted in a variety of equipment configurations and types, for example by providing a mixture of the aqueous slurry of oxidized starch with the polymer in a digester, a pressure resistant stirred vessel, an autoclave, or a kneader of an extruder. The reaction can be carried out batchwise or continuously. A jet digester (cooker) will typically be used. This can be done by continuously feeding an aqueous mixture of oxidized natural starch and polymer to a jet digester; however, alternatively an aqueous slurry of oxidized starch and separately an aqueous solution of a polymer can be introduced continuously into the jet cooker or digester. Typically, it will be preferred to at least have mixed the polymer solution with the aqueous starch slurry in a mixing chamber before introducing them into the jet digester. The mixing chamber used for the (turbulent) mixing may be, for example, a binary or multi-medium nozzle. The conditions can be selected such that the residence time of the substances to be mixed will be, for example, from 0.08 to 1 second, preferably from 0.1 to 0.5 second. After leaving the mixing chamber, the mixture would typically be directed through a digester, which may be, for example, a heating coil which would be kept at the reaction temperature with the aid of an oil bath. The reaction product could then let down via a pressure limiter and be cooled to about room temperature.
The reaction temperatures for forming the adducted combination will typically be within the range of 80xc2x0 to 1 80xc2x0 C., preferably 110xc2x0 to 160xc2x0 C. and in most instances will be within the range of 120xc2x0 to 150xc2x0 C. At temperatures of the reaction mixture above 100xc2x0 C., the reaction will typically be carried out under pressure.
In general, under the preferred conditions identified in the previous paragraph, the reaction of the starch with the polymer will be carried out over a period of from 5 second to several hours, typically from 10 seconds to 20 minutes, depending on the specific temperature. The reaction can usually be effected at up to 180xc2x0 C. under pressure conditions of up to 10 bar, but may also be carried out at above 10 bar, for example at from 11 to 80 bar and above the gelatinization temperature of the starch. The polymer modified starch is typically obtained in the form of particulate aggregates dispersed in water. The particulate structure of the starch polymer complexes generally leads to milky opacity of the reaction product. The size of the particulate aggregates (i.e., the mass median particle diameter) will typically be, for example, 0.1 to 100 xcexcm, usually within the range of 1 to 45 xcexcm. The mass median particle diameter of the polymer modified starch will be, in most cases, within the range of 2 to 35 xcexcm. The mass median particle diameter of the polymer modified starches can be determined with the aid of static light scattering, for example, with an apparatus provided by Coulter Corporation, Miami, Fla.
Polymer modified starch compositions according to the present disclosure are usable is wet end additives in papermaking processing. In general, they would be used in place of conventional starch or modified starch additives. However, they can be used in manners that provide significant advantage.
First, their characteristics are such that they can be effectively used in rather significant amounts, without undesirable effects with respect to drainage, commonly seen with many starch additives.
In addition, they can be used in manners achieving relatively high starch retention, with conventional equipment and processing techniques.
Indeed, the nature of the polymer modified starch additives according to the present disclosure is such that they can be incorporated in relatively high amounts, in a wet end process, without undesirable effects on paper processing, such as creating inefficiency or slower processing. For example, the starch additives according to the present disclosure can be incorporated in amounts on the order of 2%-9%, by wt. based on dry wt. of resulting paper.
Indeed, it has been found that in some instances the amount of starch modifier that can be provided in the paper at the wet end of the process, using a polymer modified starch additive according to the present disclosure, is so high, for example at or above 4%, (or typically at or above 6%) by wt. of paper, that a size press operation downstream from the wet end processing, can be entirely eliminated from the papermaking process. This can be highly advantageous, in terms of production efficiency for a papermaking process. This can be especially helpful in papermaking processes that involve the utilization of relatively high amounts of recycled fiber materials.
In general, polymer modified starch compositions according to the present invention can be incorporated in the wet end of a papermaking process utilizing conventional techniques and processing equipment. It is noted, again, that modification from standard techniques can be implemented, if desired, to obtain relatively high amounts of starch inclusion in the wet end process, if desired, to an effect high enough to avoid the use of a size press operation.
In some instances, the polymer modified starch material will be prepared and shipped as a commodity to the papermaking facility. In general, this will be referred to as a one component process. In other instances, the starch component and the polymer component will be reacted at the papermaking facility, typically in the jet cooker or similar starch cooking operation, prior to addition to the wet end of the papermaking process. Two variations in this approach would typically be used. In a first, a one component process, the starch/polymer combination would be pre-made and shipped to the papermaking facility, but not be pre-reacted, by merely mixing the two components together and providing a mixture fed into the starch cooking operation which has conditions appropriate to facilitate reaction between the starch component and the polymer component. For the second, the starch component and the polymer component would not be pre-mixed, but would be fed into the starch cooking process of the papermaking facility separately, with reaction occurring in the starch cooking operation, typically in a jet cooker.
In general, the principles described herein also relate to paper products characterized by presence therein of a paper modifying effective amount of a polymer modified starch composition as characterized herein. In general, the term xe2x80x9cpaper modifying effective amountxe2x80x9d may be used as a reference to an amount of component adequate to provide modification of paper properties, relative to its absence. Typical paper properties that can be monitored for this effect would be burst strength or tensile strength.
In typical applications, the amount of polymer modified starch composition included would be at least about 1% by dry wt. paper, typically 2%-9% by wt. based on dry wt. of paper.
In the context of referring to the amount of polymer modified starch composition included in the wet end of a papermaking process, or the paper on a wt. percent of dry paper wt., reference is meant to a theoretical calculated wt. percent of the polymer modified starch composition or additive, assuming all starch particles are covalently interacted with polymer molecules. It is recognized that the polymer modified starch composition, as indicated above, could well comprise a mixture of: unreacted starch; unreacted polymer; only ionically reacted starch/polymer; and, starch/polymer combination which has been at least covalently interacted.
The identified compositions for the production of paper are preferably used as dry strength agents. Known paper, paperboard and cardboard qualities, for example writing, printing and packaging papers can be produced. The papers may be produced from a large number of different fiber materials, for example from sulfite or sulfate pulp in the bleached or unbleached state, groundwood, waste paper, thermomechnical pulp (TMP) and chemothermomechanical pulp (CTMP). The pH of the stock suspension is typically from 4 to 10, preferably from 6 to 8.5. The dry strength agent may by used both in the production of base paper for papers having a low basis weight (LCW papers) and for cardboard. The basis weight of the papers is typically from 30 to 200, preferably from 35 to 150 g/m2, while that of cardboard may typically be up to 600 g/m2. The dry and wet strength agents can also be applied to the surface of paper to improve paper strength. Compared with papers produced in the presence of an equal amount of natural starch, the paper products produced according to the current disclosure can be produced to have markedly improved strength, which can be quantitatively determined, for example, on the basis of one or more of the burst strength, the bursting pressure, the CMT value and the tear strength.
According to yet another aspect of the present disclosure there are provided processes for determining the level of modification of a lightly oxidized and/or negatively charged starch comprising one or more of the following tests:
reacting the starch with Tollen""s reagent,
reacting the starch with dinitrophenylhydrazine,
titrating the starch with a suitable indicator, preferably phenylphthalein.
According to another aspect of the present invention there are provided processes for determining the presence and/or relative amount of carbonyl groups in oxidized starch comprising the steps of:
(a) exposing the starch to a carbonyl group marker, typically an aldehyde marker, preferably fluorescein-5-thiosemicarbazide; and, subsequently,
(b) analyzing the starch for the presence of marked carbonyl groups by one or more of the following types of analyses:
CLSM chemical imaging,
Raman chemical imaging, and
SEM imaging.
In this section, the parts and percentages reported are by weight, unless otherwise indicated.
A. General Principles and Observations Regarding Starch Treatments and Starch Analyses
1. Starch Treatments
1.1 Hypochlorite Oxidations
For a typical hydrochlorite oxidation, the starch is oxidized in an environment, wherein the available chlorine is about 0.005 to about 3% available chlorine by weight of starch, preferably 0.05 to about 2% available chlorine by weight of starch, and preferably more from about 0.15 to about 1.5% available chlorine by weight of starch. During a typical hypochlorite oxidation, in an aqueous medium, the pH range of the suspension is maintained from 2 to 12. As will be seen from experiments below, in some instances the oxidation is conducted under alkaline conditions, by conduct in an NaOH solution. A typical hypochlorite oxidation is conducted at a temperature within the range of 10xc2x0 to 50xc2x0 C.
1.2 Periodate Oxidations
For a typical periodate oxidation, the starch is oxidized, for example in an aqueous environment, wherein the periodate is present at about 0.01%-5% by weight of starch, preferably 0.1 to about 3 wt. %, even more preferred 0.3 to about 3 wt. % periodate by weight of starch; with a pH range of the suspension within the range of 1-8; and, at a temperature within the range of 10-50xc2x0 C.
2. Starch Analyses
2a Brabender Viscosities
For Brabender viscosity measurements, the starch slurry is heated in a Brabender viscoamylograph under constant rate of shear (75 rpm) and the increase of viscosity is measured as torque (BU) on the spindle and a curve is traced. The temperature profile is as follows: start temperature at 50xc2x0 C.; rate of heating 1.5xc2x0 C./minute until a temperature of 93xc2x0 C. is reached (phase 1) and holding the temperature at 93xc2x0 C. or 30 minutes (phase 2). Subsequently, the cooling starts at a rate of 1.5xc2x0 C./minute until a temperature of 50xc2x0 C. is reached (phase 3) and holding at 50xc2x0 C. for 30 minutes (phase 4). The viscosity is measured during this temperature program. Peak viscosity is the maximum viscosity of the first peak in phase 1. Hold viscosity is the viscosity at the end of the hold time of 30 minutes at 93xc2x0 C., phase 2. The setback is the viscosity at the end of the cooling period (phase 3) at 50xc2x0 C. (=the start of the hold at 50xc2x0 C., phase 4).
The data reported in Tables A and B below for various modified starches were measured at pH 4.5 at a starch slurry concentration of 7%. In the tables, BU means Brabender Units.
The procedure used for preparation of the Table A examples, is that described for hypochlorite oxidation in Experiment 1 below, except modified for the amount of available chlorine, as defined.
For the example in Table B, the procedure of Experiment 2 below was used.
2b Carboxyl and Carbonyl Bulk Analyses
In general, carboxyl and carbonyl bulk analyses of modified starch are conducted by following the Experiment 7 and 8 procedures described below. In Table C, measurements of carboxyl and carbonyl presence, in modified corn starches, are reported. The carboxyl measurements were taken using the potentiometric technique of Experiment 8, converted to microequivalents. The carbonyl measurements were by the Tollen""s test, Experiment 7a.
The first two oxidations identified in Table C above (i.e., at 0.5% available Cl and 1% available Cl) were hypochlorite oxidations conducted in accord with the procedure of Experiment 1 below, except where necessary adjusted for the amount of available chlorine presence. The sodium periodate oxidation, was conducted in accord with the procedure at Experiment 2 below, except modified for % oxidant. The chloroacetic acid procedure, is a carboxymethylation procedure reported below at Experiment 3. It is noted that the hypochlorite procedure generates both carboxyl and carbonyl groups. The sodium periodate oxidation, on the other hand, does not result in oxidation to carboxyl groups, but only to carbonyl groups. The chloroacetic acid procedure is not an oxidation at all, but rather is an xe2x80x9ceffective oxidationxe2x80x9d to only provide carboxyl, since the result is the addition, to the starch, of a moity (i.e., carboxymethyl group), which itself carries the carboxyl group, but no carbonyl.
2c Particle Size Distributions
In some instances, the mass median particle diameter of the polymer modified starch was determined with an apparatus LS 130 of Coulter Corporation, Miami, Fla. 33196. The principles of measurement are described in handbook of product no. 4237214A, chapter 4 (1994) of Coulter Corporation. The measurements were carried out at a wavelength of 750 nm in aqueous solution having a solids content of 0.002% by weight of polymer modified starch. The optical model of Fraunhofer diffraction was used to calculate the particle size distribution from the light scattering profile.
In other instances the mass median particle size diameter of the polymer modified starch was determined with a Malvern Master Sizer 2000 (APA 2000). The measurements were carried out at wavelengths of 632.8 and 450 nm in aqueous soln.
In the experiments, particle size distributions measured with the Melvern Particle Sizer for the adducted combinations, after cooking, were typically in the range of 0.1 to 12 micrometers.
B. Some Observations Regarding a Particular Polymer Modified Starch
As the result of investigations conducted thus far, a preferred polymer modified starch composition, for utilization as a paper additive, is a combination of starch and a polyvinylamine (PVAm). A specific such additive, described below, is an adducted combination of: (a) starch which has been oxidized with 0.5% available chlorine by wt. of starch (Cargill product C1500); and, (b) polyvinylamine (PVAm); the particular preferred PVAm being as described below at Experiment 5, for Polymer 1.
Preferred such combinations have been found to be ones wherein the amount of polymer combined is about 0.5-2%, by wt. of starch component combined.
C. General Manufacturing Procedures for Polymer Modified Starch Usable, for Example, in the Paper Industry
As characterized more briefly above, a result of the investigations conducted, two general approaches to preparing polymer modified starch, for example, for use in the paper industry, have been developed. Herein the two general approaches are: one component approaches; and, two component approaches. In general, in a one-component approach, the combination of starch and polymer is prepared prior to shipment to the paper mill or entering into the papermaking process. Two component approaches including bringing the starch and the polymer to the paper mill separately from one another and combining them at the paper mill.
Herein, two general approaches to one component systems are described. In the first, the combination of modified starch and polymer is provided as an adducted or reacted combination, for example in accord with the definitions provided above. In the second, the combination of the modified starch and polymer is provided in a mixed form of the materials, unreacted, but in a form that will react to form adducted or reacted combination when appropriately introduced into processing in a paper mill, for example when introduced into a jet cooker. Variations in these two general types of one component approaches are provided in more detail, below.
For a two component approach, typically the polymer and the starch are directed into the papermaking operation separately, and the polymer modified starch is prepared in the papermaking process. An example of this was characterized above, for example in the description wherein separate streams of polymer and starch were described as directed into a jet cooker, and reacted in the jet cooker to create the adducted combination.
One Component Manufacturing Procedures
During the present investigations, several different categories of one component manufacturing procedures were defined. In general, the different approaches are characterized with respect to the state of the oxidized starch, or the state of the polymer (typically PVAm), introduced into the procedure to form the combination, prior to introduction of the combination into a papermaking process. For many of the procedures, the definitions turn on the amount of solids (versus water) in each of the two components that are adducted, to form the adducted combination.
In general, five general procedures have been defined as follows:
1. Wet-wet procedure;
2. Semi dry-wet procedure;
3. Dry-wet procedure;
4. Dry-dry procedure; and
5. Pre-gel procedure.
In procedures 1-4 in the above list, the first characterization refers to the state of the starch component (typically oxidized starch) prior to mixing with the polymer to form the combination; and, the second characterization refers to the state of the polymer (typically PVAm), prior to mixing to form the combination. As will be apparent from the following, procedures 1-3 form adducted combinations. However, procedure 4 forms a non-adducted combination; i.e a mixture which is in an appropriate form to react to an adducted combination, when appropriately treated for example during a papermaking operation.
In the following table, examples of procedures 1-4 are provided with an indication of the water contents and the state of the materials or components mixed, to form the combination.
Herein the term xe2x80x9cwetxe2x80x9d when used in reference to the starch component, refers to a slurry which contains less than 50% starch solids (dry wt.). A PVAm/water combination is referenced as xe2x80x9cwetxe2x80x9d if the PVAm is in solution. As an example, for a wet-wet process, the starch would be oxidized by adding hypochlorite to a 40%, based on dry solids, starch slurry. After starch oxidation, PVAm solution would be added to the starch slurry. To prevent part of the PVAm being lost, the next steps would typically include drying the total system and inducing reaction between the starch and PVAm (for example, with heat) before and/or during drying.
When the slurry is heated, the PVAm and starch will react, to form the adducted combination. This can be observed by a change in viscosity and particle size distribution. Heating the slurry can be a separate step or combined with the drying step. Usable drying steps include, for example drum drying, spray drying, flash drying or ring drying.
From the above, it is apparent that there are a variety of options for conducting a wet-wet process. As a first option, once the mixture of oxidized starch and PVAm solution is made, it can be dried without a separate heating step, using the process of drying to induce reaction. As a second option, once the oxidized starch slurry in the PVAm solution are mixed, there would be separately heated to a temperature below the cooking temperature of the starch. After this, a drying step would be conducted.
As a third option, once the oxidized starch slurry is mixed with the PVAm solution, the mixture would be heated in a reactor (for example, a jet cooker or extruder) to a temperature range of about 40xc2x0 C. to 180xc2x0 C., for example, 60xc2x0 C. to 160xc2x0 C. and it is foreseen most typically from 100xc2x0 C. to 150xc2x0 C. with a follow-up step of drying. The difference between the third and the second options is that the second option would typically be conducted in the slurry tank containing the oxidized starch slurry, whereas the third option involved moving the mixture to a separate reactor and in typical instances would be above the cooking temperature of the starch. The third process is similar to that which would be used in a two-component system, except conducted separately from a papermaking operation.
Herein, the term xe2x80x9csemi-dryxe2x80x9d when used in reference to the starch composition, is meant to refer to starch composition which has a dry solids content of about 50 to 80%, typically about 66%. Such a composition would typically result from de-watering the oxidized starch slurry resulting from the oxidation process, for example, by filtration or centrifuging, decanting, and/or pressing. A typical approach would be to use a filter press, to generate a filter cake with a dry solids content in the range specified.
In a typical semi-dry wet process, the semi-dry oxidized starch filter cake would be sprayed, with a PVAm solution, for example, in a continuous or batch mixture (usable equipment including, for example, a paddle mixture, a high shear mixture, a plow blade mixture, or a ribbon blender). The mix cake would be dried in a ring dryer or similar dryer. Typical and preferred drying conditions would be with an inlet temperature of about 110-250xc2x0 C., and an outlet temperature of about 60-65xc2x0 C. The result would be an adducted combination.
In general, in reference to an oxidized starch composition, the term xe2x80x9cdryxe2x80x9d is meant to refer to a composition that has a dry solids content of greater than 80%, by wt. Typical compositions will have a dry solids content of 80% by wt. or greater.
An example of preparation of a dry oxidized starch, would be taking a starch slurry prepared, for example, by starch with a hypochlorite in a 40% dry solids starch slurry, and after reaction centrifuging or filtering the slurry to a filter cake of about 66% dry solids modified starch. The starch cake could then be further dried in a dryer (for example, a ring dryer) up to a dry solids content of above 80%, for example, 98%.
The adducted combination would then be prepared by spraying a PVAm solution over the dry starch, followed by another drying step. Spraying and drying can be performed in one step, for example, in a floating or fluidized mixer-dryer combination.
The result of processing described in the three options discussed before, will typically be a one-component system of adducted combinations, in the form of agglomerates. By heat treatment (up to for example 50xc2x0 C. for ten minutes to several hours) and/or sheared with a high shear mixture, the agglomerates can be disrupted. Disrupted agglomerates are generally easier to cook in a papermaking operation, than agglomerates still intact. However, disruption of the agglomeration is not a necessary step, for use in a papermaking operation.
For the options described thus far, generally the PVAm component is used in solution, and the result after addition to the starch component, and application of heat, its reaction to form the adducted combination. Alternatively, the PVAm can be provided in a dry state, and mixed with the dry starch component. The result will be an unreacted mixture or combination. The combination, however, would be such that the reactive polymer component will react with the oxidized starch, once heat is applied. Thus, the mixture is one which when introduced to the starch cooking step of a papermaking operation, will form an adducted combination.
Pre-gelled Systems
With pregelled systems a one-component system is defined that was heat treated during manufacturing in such a way that the starch was partly or completely gelatinized. It can be theorized that an advantage is that it becomes easier to cook in the paper mill. In some instances, the starch will be sufficiently cooked to be cold water dispersible, and if cold water dispersible, no cooker is required in the paper mill before application.
Storage of the Various One Component Systems; Characteristics and Use
For a typical one-component system, whether it comprises the adducted combination or the dry components mixed together, the optimal storage will typically be between xe2x88x9210xc2x0 C. to +80xc2x0 C., preferably at about 10xc2x0 C.-25xc2x0 C.
Preferably the one-component system will be maintained at a moisture content of no greater than about 12%, usually about 6 to 12%. Typically, the moisture content will be 9-12%.
In general, the one component system will comprise agglomerates, i.e., starch agglomerates. The agglomerates will be formed by agglomeration of several starch or modified starch granules. The agglomerate sizes are typically 3 to 20 times bigger than the starch granules size. The agglomeration becomes stronger, as the moisture content increases. Thus, agglomeration increases with storage time, especially if humidity is high. If the agglomeration is dispersed in water with shearing and/or heating, the agglomerates can be disrupted. The Brabender viscosity will in general depend on the manufacturing of storage conditions. In Table E below, typical Brabender viscosities for typical one component systems are presented.
D. Use of a One Component System in a Papermaking Operation
As indicated briefly above, in general, one component systems according to the present disclosure can be handled, in the wet end of a papermaking operation, similarly to utilization of conventional starch compositions. Of course, if the one component system used resulted from a dry-dry operation, the chemical interaction to provide the adducted combination would not yet have occurred. With such systems, it can be expected that reaction to the adduct typically will be initiated in a cooking operation as the starch is cooked for use in the papermaking process.
The performance of the composition in paper can be dependent on the particle size distribution of the starch dispersion. By manipulation of the cooking conditions it is possible to obtain a desired particle size distribution and to change the performance in a papermaking operation.
The cooking conditions can be manipulated by changing, for example, residence time in the cooker, temperature, concentration of the starch slurry and shear applied during cooking.
In the typical papermaking process, and to advantage, standard cooking conditions for starch can be utilized, with one component systems according to the present disclosure. Typical conditions will be as follows:
1. Use as the cooking device or reactor, an autoclave, extruder, stern vessel, jet cooker, high shear cooker (for example with a rotating tooth and chamber set), or heat exchanger;
2. Conduct of the cooking operation in either a continuous or batchwise manner;
3. Slurry concentration during cooking of 1-15%, typically 4-12%, preferably 6-10% based on wt. % starch in water; and
4. Cooking temperatures of 80-180xc2x0 C., typically 100-160xc2x0 C., preferably 100-150xc2x0 C., with residence time of ten seconds to thirty minutes, depending on such parameters as temperature, shear, and concentration.
After cooking, if the system is one in which the oxidized starch (or otherwise modified starch) and the PVAm (or other polymer) were not reacted prior to production into the cooking system, the reaction to the PVAm and the starch could be allowed to proceed over a period of time typically, for example, from about five seconds to several hours, preferably with conditions chosen such that the reaction to adduct will be completed within time of from 10 seconds to 20 minutes, and prior to addition of the material to the paper.
It is anticipated that in typical systems prior to addition to the pulp, the polymer modified starch composition will be diluted to a final starch concentration of 0.05-5%, preferably 1-3%.
Of course, the water for the slurry preparation and dilution can be fresh water or water from a closed water system in the paper mill.
E. Utilization of Oxidized Starch and Polymer (For Example PVAm) as a Two Component System in a Papermaking Operation
Typically, if utilized in a two component process, the oxidized starch (or otherwise modified starch) and PVAm (or other polymer) are introduced separately into the papermaking operation, for example, through separate introduction into the cooking operation. The cooking can be performed in accord with the conditions described above, in connection with general cooking conditions for one component systems. It will generally be required that the conditions be selected such that adequate time for interaction between the oxidized starch and the PVAm is provided.
In general, there are three options for bringing together the starch and the polymer (PVAm) at the paper mill; these would be before, after, or during cooking of the starch.
If they are brought together before the cooking of the starch, the system would be similar to the process described above for utilization of a dry-dry combination. That is, the materials we brought together, either in slurry or in dry form, and would be provided in an appropriate slurry form for cooking as a starch. In a typical approach, the mixing of the starch with the PVAm (or other polymer) would be in a makeup tank or inline, with the mixing for cooking being conducted within an appropriate time frame for the system management, for example, 0.08 seconds to several hours. It would typically be preferred for a paper mill operation, that the mixing be conducted in a short time frame, for example, 0.1 seconds to 1 minute. The resulting dispersion would then be cooked, and fed to the pulp or, if desired, allowed to react for several hours prior to addition to the pulp.
In the second approach, the PVAm (or other polymer) would be added to the reactor during the starch cooking. The resulting dispersion would then be added to the pulp, or, if desired, allowed to further react, for example, up to several hours before addition to the pulp.
In the third option, the starch slurry would first be cooked, and then the PVAm (or other polymer) solution would be added to it. For this approach, reaction time will typically be 10 sec to 20 min, before addition to the pulp.